1. Field of the Invention
This invention relates to a process and apparatus for forming cold finished bar from hot rolled round and more particularly to a process and apparatus for removing the mill scale from hot rolled round to form cold finished bar.
2. Description of the Prior Art
In the manufacture of steel products it is the practice to remove the mill scale from the surface of the steel by one operation and to perform the final size reduction and finishing by another operation. Mill scale may be removed either mechanically or chemically. Known mechanical processes include sandblasting, grinding and the like, as well as passing the workpiece through a descaling machine. A typical descaling machine is manufactured by Pangborn Corp. and is operable to remove mill scale from rod, sheets, billets, slabs and other steel products by feeding the item through a descaling chamber where abrasive streams of shot and/or grit are directed onto the entire surface area of the workpiece. The abrasive streams remove the scale from the surface of the steel. However, the steel must be fed through the scaling chamber at a relatively slow rate to ensure that all the mill scale is removed in a single pass so that it is not necessary to make more than one pass through the descaling chamber.
Chemically, mill scale is removed from the surface of steel stock by pickling with acid. The steel stock is immersed in an acid bath which chemically attacks the mill scale to remove it from the surface of the stock. This operation is time consuming and requires considerable floor space to accommodate the vessels for the acid bath. Furthermore, pickling is relatively expensive and presents problems in the disposal of the waste pickle liquor.
It is also known to reduce the diameter of bar stock by cold rolling or cold drawing to produce a cold rolled bar and a cold drawn bar respectively. With these operations the stock is reduced in diameter by redistributing the material of the bar in order to form a bar having a preselected size and smoothness of finish. However, prior to reducing the diameter of and sizing the round bar stock, the mill scale must be removed by one of the above mentioned operations. U.S. Pat. No. 2,642,763 discloses a cross rolling mill for reducing the diameter of and for sizing round bar stock. The cross rolling mill includes a pair of work rolls each having a concave work engaging surface that exerts a rolling force on the workpiece to reduce the diameter of the bar and shape the bar so that the bar is circular in cross section throughout its entire length and has a preselected surface finish. A backing roll supports each work roll. The backing rolls are rotatably supported and driven to exert a preselected pressure upon the work rolls to maintain the work rolls in contact with the stock to make the desired reduction of the stock.
U.S. Pat. No. 1,914,587 discloses a method of finishing rounds that includes passing the round through a longitudinally spaced series of cross rolls. The cross rolls are arranged in pairs and each pair includes an idler roller and a cooperating driven roller. The initial pair of cross rolls break the scale from the stock by pressure application, and the remaining cross rolls provide for rounding and polishing. The round is also passed through a steel blast for descaling.
U.S. Pat. No. 2,163,699 discloses a method and apparatus for rolling hot strip material that includes a roughing stand of work rolls and back-up rolls, a scale breaker of a pair of pressure rolls, and a finishing stand of work rolls and back-up rolls.
U.S. Pat. Nos. 2,242,024 and 3,081,524 disclose scale breaking apparatus for rods and wire by flexing and bending the stock to break the scale on the stock. The stock is also subjected to the scarifying action of toothed sheaves which scratch the scale from the stock.
Hot rolled round after fabrication is non-circular in cross section and by the forming and finishing process is reduced to a final preselected circular dimension. However, as the non-circular or elliptically shaped round is passed through the pressure rolls it has a tendency to skid through the rolls without rotating. Subsequently, flat spots are formed on the round and all the scale is not removed from the surface of the round if it is not uniformly rotated through the pressure rolls.
Therefore, there is need in the process of cold forming hot rolled round by pressure rolls to increase the efficiency of the work rolls to remove the scale from the round without encountering the problem of the roll skidding through the pass of the work rolls without rotating. In addition, there is need for a process and apparatus for efficiently combining the operations of removing mill scale from the surface of hot rolled round and reducing the round to form a cold finished bar in a manner that overcomes the disadvantages of separately carrying out the operations of mechanical and/or chemical descaling and finishing by cold rolling or cold drawing.